Glossary
Terms as they are used on this site. A striking number of them carry more than one meaning in ordinary industry conversation, and several disputes that look technical turn out to be two people using the same word differently. Where that is the case, the entry says so instead of pretending the matter is settled.
Abatement cost
The cost of avoiding a unit of emissions, usually quoted per tonne of carbon dioxide equivalent. Almost never comparable between sources without unpacking it: some quotes are capital only, some annualised, some net of the fuel saved, some assume a carbon price and some are what the carbon price would have to be. Ask what is in the numerator and over what period before comparing two figures.
Additionality
Whether an outcome — generation built, emissions avoided, a credit issued — happened because of the intervention claiming it, or would have happened anyway. Unobservable in principle, since it depends on a counterfactual, and therefore approximated by rules. The central weakness of every claim resting on procurement rather than on physical change.
Baseline
The reference point a reduction is measured against, usually a named year. Gets recalculated when the organisation acquires or divests assets, changes method, or corrects an error. Recalculation is legitimate and necessary; it is also the easiest place for a target to become quietly easier, which is why the policy governing it should be fixed before it is needed.
Biogenic carbon
Carbon dioxide released from material of recent biological origin, as distinct from fossil carbon. Conventionally reported separately from the main total on the reasoning that regrowth reabsorbs it. How well that reasoning holds depends on the source, the land it came from and the time the regrowth takes — none of which the accounting convention itself examines.
Calcination
Heating a carbonate mineral until it decomposes into an oxide and carbon dioxide. The core reaction in cement and lime production, and the reason a large share of those sectors’ emissions comes from the raw material rather than the fuel. Stoichiometric: the mass released per unit of oxide produced is fixed by chemistry and identical everywhere.
Calorific value
The heat released by burning a unit of fuel. Quoted on a gross (higher) basis including the heat recoverable by condensing the water vapour in the exhaust, or a net (lower) basis excluding it. Emission factors expressed per unit of energy are published on one basis or the other, and mixing bases with quantities is a routine source of error in otherwise careful inventories.
Carbon capture, utilisation and storage
Separating carbon dioxide from a gas stream and either using it or injecting it underground. The abbreviations are used loosely: some writers mean storage only, some include utilisation, and the two have very different permanence. Cost is driven far more by the concentration of the source stream than by the total quantity, because separation energy rises steeply as the gas becomes dilute.
Clinker factor
The proportion of clinker in finished cement. Lowering it by substituting other materials lowers process emissions in direct proportion, which makes it the most immediately available lever in the sector and the one most constrained by prescriptive product standards rather than by engineering.
Coefficient of performance
Heat delivered by a heat pump divided by the electricity it consumed. Above one by definition, because the machine is moving heat rather than creating it, and falling as the temperature lift between source and sink widens. The single number that decides whether electrifying a low-grade heat duty saves energy or merely relocates it.
Direct reduced iron
Iron produced by removing oxygen from ore in the solid state rather than by melting it in a blast furnace. The reducing gas can be derived from natural gas or from hydrogen; with hydrogen the reaction product is water rather than carbon dioxide, which is why this route dominates discussion of primary steel without carbon.
Electric arc furnace
A furnace that melts its charge with an electric arc. Widely used for scrap-based steelmaking, where the chemistry of reduction has already happened in a previous life of the metal, so emissions depend chiefly on the electricity supply. Also used to melt directly reduced iron.
Embodied carbon
Emissions associated with producing a product, as opposed to operating it. Boundaries vary enormously — cradle to gate, cradle to site, cradle to grave — and two embodied figures for the same material are frequently not comparable because they stop at different points. Always ask where the boundary was drawn.
Emission factor
Emissions per unit of activity: per unit of fuel, of energy, of material or of spend. Not a constant of nature. Varies by region, fuel specification, gases included, global warming potential values applied, calorific basis and whether upstream production is counted, and is revised on a publication cycle. Any figure derived from one is only as sound as the factor’s provenance.
Fugitive emissions
Releases that are not deliberate combustion or reaction — leaks from seals, valves, storage, refrigeration and gas handling. Frequently material and frequently estimated rather than measured, because measuring them means finding them first.
Global warming potential
The factor converting a quantity of a greenhouse gas into a carbon dioxide equivalent. Depends on the time horizon chosen and is revised as the science is updated, so the same physical release converts to different equivalent figures under different assessment editions. An inventory that does not state which set it used cannot be reconciled with one that does.
Grid emission factor
Emissions per unit of electricity consumed. Two conventions coexist by design. Location-based uses the average for the grid where the load physically sits. Market-based uses the factor attached to the buyer’s contracts and certificates. They answer different questions, they diverge, and reporting only the flattering one is the most common quiet omission in corporate disclosure.
Hard to abate
A label for sectors whose emissions do not respond to fuel switching alone, typically because carbon appears in the process chemistry or because the heat requirement is difficult to deliver electrically. Used loosely — it sometimes means technically difficult, sometimes merely expensive, and occasionally just means politically protected. Worth asking which sense is intended.
Heat integration
Designing a plant so that streams needing cooling supply streams needing heating, rather than rejecting heat at one point and buying it at another. Pinch analysis is the systematic method. Usually the cheapest abatement on a site and usually done last, because it touches many units at once rather than one.
Hurdle rate
The minimum return an investment must promise to be approved internally. Commonly set well above the cost of capital for efficiency projects, not out of confusion but because capital is rationed and these projects compete with capacity expansion. It quietly determines more industrial abatement outcomes than any technology choice.
Hydrogen colours
An informal palette — green, blue, grey, turquoise and others — describing how hydrogen was produced. The terms are neither standardised nor consistently applied, and they compress the only thing that matters, which is the emissions intensity of the specific production route including any capture rate actually achieved. Prefer a number and a method to a colour.
Lock-in
The condition of having committed, through a capital decision, to a level of emissions for the life of the asset. The reason the timing of rebuilds matters more than the availability of technology: a conventional rebuild forecloses alternatives until the next cycle, which may be decades away.
Marginal abatement cost curve
Measures ranked by cost per tonne abated and drawn as a staircase. Useful for communication, misleading as a plan, because it presents interacting measures as independent and is computed at one set of prices that will not hold. Sequences compared under several price paths are the more honest version.
Net zero and carbon neutral
Both describe a balance between emissions and removals, and neither is used consistently. The questions that separate a rigorous claim from a decorative one are the same each time: which scopes are covered, how much of the balance is achieved by reduction rather than purchase, what kind of instrument the remainder relies on, and how permanent that instrument’s effect is.
Oxy-fuel combustion
Burning in oxygen rather than air, so the exhaust is largely carbon dioxide and water instead of being diluted with nitrogen. The point is not efficiency but capture: it produces a concentrated stream, moving the cost from separation to oxygen supply.
Process emissions
Emissions arising from a chemical or physical transformation rather than from combustion — calcination, reduction, anode consumption. Unaffected by fuel choice, calculable by mass balance, and often more precisely known than combustion emissions because stoichiometry is exact. Some organisations fold fugitives into this category and some do not, so check what a stated figure includes.
Reductant
The substance that takes oxygen away from an ore. In conventional ironmaking it is carbon, which makes carbon dioxide a product of the intended reaction rather than a sign of inefficiency. Replacing the reductant, rather than the fuel, is what changes the emissions of primary metal production.
Residual elements
Elements that accumulate in recycled metal because they do not oxidise out during refining — copper from wiring and motors being the standard example. They place a ceiling on the share of demand that scrap-based production can serve, since some product grades cannot tolerate them and dilution with primary metal is the usual remedy.
Scope 1, 2 and 3
A classification of emissions by reporting responsibility, not by physical origin. Scope 1 is direct release from sources the organisation controls; scope 2 is purchased energy; scope 3 is everything else in the value chain, upstream and downstream. The same physical emission legitimately appears in more than one organisation’s report, which is why corporate inventories cannot be summed into a national total.
Stranded asset
Equipment retired, or written down, before the end of its useful life because regulation, prices or market demand moved. The prospect of it is a live constraint on investment decisions today, and the accounting consequence — a write-off of remaining book value — is often a bigger obstacle to early replacement than the cash economics.
Waste heat recovery
Capturing heat leaving a process and putting it to use elsewhere. The abatement that requires no change of fuel, no new energy carrier and no grid connection, and which shrinks whatever equipment eventually replaces the burner. Limited by the temperature at which the heat is available and by whether there is a matching demand nearby at the time it is produced.